The invention relates to a method for the preparation of bis(dienyl)complexes of iron group metals, such as bis(pentadienyl) complexes of iron group metals.
M(RPD)2 type organometallic complexes, in which M represents iron, ruthenium, or osmium; R represents hydrogen or an alkyl group; and PD may be a cyclic or open chain dienyl system that forms a sandwich type complex, are commonly used in processes relating to thin film formation. For example, ruthenium thin films may be used in semiconductor manufacture, where resistive or conductive layers are desired, as decorative coatings on ceramics, and in resistively heated surfaces, as in automotive windows. The electronic component literature describes conductive film formation and resistive film formation via chemical vapour deposition (CVD). For electronic devices, high purity raw materials are imperative for producing operational parts in high yield.
In the processes described in U.S. Pat. Nos. 6,002,036 and 6,642,402 for forming bis(dienyl)ruthenium complexes, zinc and magnesium, respectively, are utilized as reducing metals. Using Zn or Mg in the reaction, however, can form pentadienyl-Zn and pentadienyl-Mg impurities. Although the described prior art generally avoids water in the reaction, Kadokura (U.S. Pat. No. 6,002,036) suggests that trace water from the reactant RuCl3 hydrate is adequate to decompose any Zn(EtCp)2 that may form. However, there is no indication as to how much water is supplied by the Ru salt. Metal hydrates are generally non-stoichiometric, and typically, FeCl3, RuCl3, and OsCl3 hydrate salts vary in their water content. Accordingly, the water of hydration may be insufficient to decompose the unwanted metal pentadienyl compounds, and such impurities may still be present in the prior art complexes.
It would thus be desirable to produce the above-described M(RPD)2 complexes in high yields while ensuring that base metal impurities are minimized.